DD's favorite thing to do is "Projects!" Anything she can paint/craft/build by herself keeps her occupied for awhile.
The pre-boxed items like painting ceramic figurines or wooden things or window suncatchers are great because I can open the box and set it in front of her, and she's got the little case of paints and everything all ready to go. For these we love melissa and doug crafts. Other from the box kits we have loved included jewelry making, doll making, coloring stuffed animals, a rock dig, etc.
Projects that I set up for her go over really well to. An example is one day I rolled out a bunch of white polymer clay and gave her cookie cutters. She spent all day making shapes. That night I put little holes through the tops of each shape and baked them. The next day I gave her paints and she painted them all for hours... That day and even the two days after that. I strung string through the tops and then we had Christmas ornaments for her to give everyone this year.
Also, observable science projects have been a big hit. Again, we've had good luck with pre-boxed kits and homemade things. The biggest hit from the pre-boxed kits was rock crystals. But, DD really loved the growing projects she did indoors. She would rush every morning out of bed to check her bean sprouts. LOL But, we also planted a pineapple top, grew onions in our windowsill, took cuttings from philodendrons and purple hearts and started them in water, and srarted a celery plant. We have a fish tank that she loves to watch as well, and for the spring I'm thinking of hatching butterflies. Watching what's happening to these things takes up a lot of time, but if I'm ever in a pinch I can suggest drawing a picture of it, how it's changing, or what she thinks will happen.
Ooh! One last one that has been a lifesaver is fridge magnets! We have states, shapes, and numbers covering the bottom half of our fridge. She plays with these daily for long periods of time.